1. Field of the Invention
This invention generally relates to optical devices and more specifically to optical devices that are used in clean environments.
2. Description of Related Art
Reference is made to the following Letters Patent of the United States:
U.S. Pat. No. 4,402,572 (1983) Tsunoda et al PA0 U.S. Pat. No. 4,718,750 (1988) Forkey
In the Forkey patent, an optical coupler includes a lens in a cylindrical carrier, a body assembly and a sleeve that can slide within the body assembly. This coupler is designed to connect to a photographic or image recording device at one end and to an optical instrument at the other end. The lens and carrier can move axially within the body portion to focus an image from the optical instrument onto an imaging plane in the recording device.
These and other optical devices are quite useful during medical procedures involving optical diagnostic instruments such as endoscopes and the like. However, in such environments, it is imperative that the devices be clean. In fact, it is highly desirable that such optical devices be capable of undergoing sterilization procedures in conventional autoclaves or in liquid immersion or gaseous sterilizing facilities.
Autoclaving normally occurs in steam in the region of 270.degree. F. at pressures in the range of 30 psi. In immersion procedures, equipment is immersed in various sterilizing solutions or in ethylene trioxide and similar gaseous sterilizing agents. Each of these procedures can represent a very harsh environment for optical devices. In prior optical systems it has been necessary to seal the device against liquids. For example, in the Forkey patent fine threads and lubricants effect a seal to block fluids from entering the system. In other optical systems the lens are sealed from external liquids and are filled with a dry inert gas. However, even with these approaches, repeated sterilization processes eventually break down the seals and allow liquid to enter into the lens system. When this occurs, condensation can occur in the optical path and residual sterilizing solutions can remain in the optical path; both will distort the image.
The Forkey patent is also representative of lens systems that utilize relatively thin lenses in the optical path. The Tsunoda et al patent discloses a projection device that utilizes elongate bar lens of plastic, each with a great length along the direction of its optical axis. Plastic lens, however, are affected by moisture that can alter the refractive indices differently across the lens. Thus, the Tsunda et al patent describes a structure wherein the bar lenses are positioned in a lens holding member that is sealed at both the incidence and emergence ends by transparent and moisture-impervious members. With the lens holding member, two spaced plastic bar lenses are located along an optical axis, but are separated axially by a ring structure. This total structure is then stated to shield the plastics lenses from the outside environment.
The structure in the Tsunoda et al patent is primarily designed for use in photocopy machines and the like, not in a hostile environment such as found in an autoclave or during immersion in a sterilizing solution. The structure in the Forkey patent, while sealing the optical path from the external environment is complex to make and can only withstand a limited number of sterilizing procedures.